System Management Microcontroller
applications that cannot afford downtime. Alternatively, it
Password
The device is programmed with a default password
prior to being shipped. The password is defined as the
16 words of physical program memory at addresses
0010h–001Fh. A single password lock bit (PWL) is
implemented in the SC register. Once a new device is
programmed, a password is defined (password is other
than all zeros or all ones) and the PWL bit is set. If the
PWL is zero, the device is deemed unprogrammed. The
password is automatically set to all ones following a
mass erase.
allows the application to develop custom loader software
that can operate under the control of the application soft-
ware. The utility ROM contains firmware-accessible flash
programming functions that erase and program flash
memory. These functions are described in detail in the
MAX31782 User’s Guide.
System Timing
The device generates its 4MHz instruction clock (MOSC)
internally using a ring oscillator. On power-up, the output
of the oscillator (which cannot be accessed externally) is
Stack Memory
A 16-bit, 16-level internal stack provides storage for
program return addresses and general-purpose use.
The stack is used automatically by the processor when
the CALL, RET, and RETI instructions are executed and
interrupts serviced. The stack can also be used explicitly
to store and retrieve data by using the PUSH, POP, and
POPI instructions.
disabled until V
rises above V . Once this threshold
DD
BO
is reached, 1000 cycles are counted (~ 250Fs) and then
the output is enabled, clocking the device.
System Reset
The device features several sources that can be used to
reset the device.
On reset, the stack pointer, SP, initializes to the top of the
stack (0Fh). The CALL, PUSH, and interrupt-vectoring
operations increment SP, and then store a value at the
location pointed to by SP. The RET, RETI, POP, and POPI
operations retrieve the value at SP and then decrement SP.
Power-On Reset
An internal power-on-reset (POR) circuit is used to
enhance system reliability. This circuit forces the device
to perform a POR whenever a rising voltage on V
DD
climbs above V . When this happens the following
POR
events occur:
Programming
•ꢀ Allꢀregistersꢀandꢀcircuitsꢀenterꢀtheirꢀresetꢀstate
The flash memory of the microcontroller can be pro-
grammed by one of three methods: in-system pro-
gramming, in-application programming, and production
programming. All three methods provide great flexibility
in system design and reduce the life-cycle cost of the
embedded system.
•ꢀ TheꢀPORꢀflagꢀ(WDCN.7)ꢀisꢀsetꢀtoꢀindicateꢀtheꢀsourceꢀ
of the reset
•ꢀ Codeꢀ executionꢀ beginsꢀ atꢀ locationꢀ 8000hꢀ whenꢀ theꢀ
reset condition is released
Brownout Detect/Reset
The device features a brownout-detect/reset function.
Whenever the power monitor detects a brownout condi-
In-System Programming
An internal bootstrap loader allows the device to be pro-
tion (when V
< V ), it immediately issues a reset
2
DD
BO
grammed over the JTAG or I C-compatible interfaces.
and stays in that state as long as V
remains below
DD
As a result, system software can be upgraded in-system,
eliminating the need for a costly hardware retrofit when
software updates are required.
V . Once V voltage rises above V , the device
BO DD BO
waits for t
before returning to normal opera-
SU:MOSC
tion, also referred to as CPU state. If a brownout occurs
during t , it again goes back to the brownout
Programming source select (PSS) bits in the ICDF
register determine which interface is used for bootload-
SU:MOSC
state. Otherwise, it enters into CPU state. In CPU state,
the brownout detector is also enabled. On power-up,
the device always enters into brownout state first and
then follows the previously mentioned sequence. The
reset issued by brownout is the same as POR. Whatever
action happens on POR also happens on brownout
reset. All the registers that are cleared on POR are also
cleared on brownout reset.
2
ing operation. The device supports JTAG and I C as
an interface corresponding to 00 and 01 bits of PSS,
respectively.
In-Application Programming
The in-application programming feature allows the
microcontroller to modify its own flash program memory.
This allows on-the-fly software updates in mission-critical
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